Yeast is one of the most commonly used biological systems for trace element enrichment for human nutrition and animal feed. Selenium enriched yeast along with synthetic selenomethionine and inorganic selenium salts are used for Se supplementation. The majority of selenium in selenium enriched yeast is selenomethionine a non-canonical amino acid, analog of methionine. However the chemical form of the remaining 30% of the Se in these yeast formulations are largely unknown. There are many reports in the peer reviewed literature describing other sulfur analogs of selenium in yeast however only one single paper claims that these “other Se species” (manly thiol analogs: selenols) are actually representing the “missing” 30% of selenium.
There is an ever growing interest in the synthesis of nanomaterials due to their physical, chemical and photoelectrochemical properties (Gericke, 2006). The synthesis of nanomaterials over a range of chemical composition and high monodispersity is still challenging in material science. Many of the technologies available for the production of nanomaterials are chemically and often energetically intensive. Biological production of these nanomaterials could represent a green alternative to the synthetic protocols used nowadays. It has been known for decades that many biological systems from plants to uni-cellular organism can accumulate large quantities of metallic elements (Gericke, 2006). The entire field of bioremediation is based on this notion. Plants such as those from genus Salicornia can collect Se from marshlands and volatilize it. Other plants, such as Pteris vittata (Ma, 2001), accumulate enormous quantities of arsenic, uranium, etc. forming insoluble inorganic deposits in the extracellular space effectively detoxifying them.
The use of microorganism for the intra or extracellular production of nanomaterials has been recently reviewed by Mandal et al. (Mandal, 2006). Bacteria has been reported to produce gold, silver, cadmium sulfide, magnetite nanoparticles, and, certain yeast species have been reported to produce cadmium and lead sulfide nanoparticles (Dameron, 1989; Krumov, 2007), where Cd starts and ends in the +2 oxidation state.
Inductively couple plasma mass spectrometry is the analytical tool of choice in trace and ultra trace metal analysis. However, like most mass spectrometry based wet chemical analytical strategies, ICP MS is usually used for bulk analysis. Typical sample sizes are in the milligram to gram range. When spatial resolution requires smaller sample sizes the analytical sampling and sample introduction typically moves away from wet chemistry and employs for example lasers for sampling and sample introduction. Laser ablation (LA) ICP MS is able to provide spatial resolution in the 5-10 micron range enabling applications such as tissue imaging in the biological realm. Recent developments in near field laser ablation could result in even sub-optical resolutions. However in order to study subcellular distribution of trace elements and potentially nanoparticles, submicron spatial resolution is necessary.
There remains a need in the art for a simple, environmentally friendly method of producing bulk quantities of nanoparticles, especially selenium nanoparticles.